PIP COURTNEY, PRESENTER: This story is about a possible looming revolution in the oyster industry. For more than a quarter of a century, the Pacific oyster from Japan has reigned supreme in South Australia. But the threat of a deadly disease is now prompting farmers to look at diversifying, and as Kerry Staight reports, some believe the native angasi oyster could be the answer.

KERRY STAIGHT, REPORTER: Coffin Bay on the Eyre Peninsula in SA is a haven for recreational fishers. But at the boat ramp, there's plenty of business mixed with pleasure, as a steady stream of local oyster growers come and go.

Among them is Brendan Guidera, who has been farming these waters for about 15 years. While they're home to some of the best Pacific oysters in the country, today he's heading out to harvest something a little different: his prized angasis.

BRENDAN GUIDERA, PRISTINE OYSTERS: It's a smallish part of our business, so it's something we do on the side and it's just an interesting oyster. It's the fact that it is our local oyster and it's a very good one.

KERRY STAIGHT: The angasi may be foreign to many, but back in the 1800s, this native oyster was doing a roaring trade, with around 6 million harvested annually. There were no hanging baskets or farms; the wild stock was simply scooped off the sea floor.

But after a few decades of over-fishing, there wasn't much left to pick up and the industry faded.

Brendan Guidera is leading the charge to revive it, although things didn't get off to a great start.

BRENDAN GUIDERA: The first ones we got was in about 2007. We got about 10,000 oysters and a week later we'd killed half of them just by treating them exactly the same way as we'd treat a Pacific oyster. We had them up a little bit too high at a rough time of year and learnt the hard way there.

KERRY STAIGHT: Have you also tried to grow them how they're traditionally grown, on the bottom?

BRENDAN GUIDERA: We did an experiment last year with that and then we noticed about two weeks later stingrays had eaten nearly all of them.

KERRY STAIGHT: His solution is somewhere in between. The younger angasis spend longer underwater where they're more protected. When they mature, he brings them closer to the surface, where they're exposed to the elements. As well as helping with the cleaning and fattening process, this strengthens the oyster's muscles, so the shells stay shut at harvesting, which is pretty important when it comes to shelf life.

So this is what people are probably a bit more used to, the Pacific oyster. How different is the angasi?

BRENDAN GUIDERA: It's different in the shape. These ones are very flat. The meat texture's a lot firmer and they're a lot more of a chewy - chewier flesh to eat. That's a much stronger flavour. It'll linger on the back of your palate for about five minutes after you've eaten it. An angasi in good condition, I'll prefer over a Pacific any time, but they are a much more difficult oyster to grow and we've got quite a bit to learn.

KERRY STAIGHT: Brendan believes it's a lesson well worth learning. Domestically, these flat oysters fetch twice as much as Pacifics, with the demand mainly coming from high-end restaurants. The problem is at the moment it takes longer to get to this stage.

BRENDAN GUIDERA: They take twice as long to grow and you get twice as much, but you kill a lot more than what you generally would with a Pacific. So, even though you're charging double, you're not making the same money as what you would be if you were growing just Pacifics.

KERRY STAIGHT: Send them further afield and the money-making prospects improve.

Brendan has already got buyers in Japan and Hong Kong, but his most lucrative market could be Europe, especially France, where flat oysters command three to five times the price of Pacifics.

BRENDAN GUIDERA: Their native flat oyster is identical in flavour and appearance to ours. That used to be their main oyster up until the early '70s, and as they get rarer and rarer, they also become more sought-after in a way.

KERRY STAIGHT: At a major food festival in Adelaide, the French connection is tested out in a room full of foodies and high-profile cooks.

Brisbane-born chef James Henry runs a restaurant in France where he often serves the local flat belon oyster. But today he's cooking with Brendan Guidera's angasis and he agrees they're very similar, right down to the DNA.

JAMES HENRY, CHEF: These angasi, I find them delicious. They have all the characteristics of an excellent oyster. They're briny, they have nice minerality and a bit of iodine and they're a little dirty as well, you feel like you taste where they're grown.

KERRY STAIGHT: Heading back out to where they're grown are Jill Coates, the president of the state's Oyster Growers Association, and son Jed. Their family helped pioneer the Pacific oysters boom around Coffin Bay in the '80s.

They're now following their neighbour's lead and giving angasis a go.

JILL COATES, SA OYSTER GROWERS ASSOC.: The market tells us that there's a good opportunity. The supply isn't there, so the time is right, really.

KERRY STAIGHT: The family is experimenting with different types of baskets to see what works best.

And as they near their first harvest, albeit a small one, Jill Coates says there are strong signs others are keen to give the local shellfish a look-in.

JILL COATES: We now have about two-thirds of growers with an angasi endorsement on their licences and that's a really good critical mass to give confidence to the commercial hatcheries to invest in producing spat because the demand will be there.

KERRY STAIGHT: That's where the South Australian Research and Development Institute, or SARDI, comes in. Until enough commercial hatcheries come on board, it's filling the gap by producing the baby oysters, or spat. Like at any shellfish nursery, algae production is an essential part of the operation.

These particular filter feeders also need a gentler touch.

XIAOXU LI, SARDI: The angasi spat is more sensitive than Pacific oyster because they have a thin shell.

KERRY STAIGHT: Size is definitely an issue for the juvenile angasis; not just how thin they are, but also how fast they grow.

XIAOXU LI: We trying to get uniformity growth as much as possible, but because we haven't done any selection on this component, so they growing all over the place.

BRENDAN GUIDERA: The spat that we get for the Pacific oysters, there's several hatcheries doing millions and millions. They've fine-tuned the genetics. They can easily cull the runts and the top growers out. Whereas we've had to pretty much take whatever we can get out of a handful of oysters.

KERRY STAIGHT: Someone who would like to help change that is Rodney Grove-Jones. While most Pacific oyster spat comes from Tasmania, he runs the only commercial oyster hatchery in SA, near Coffin Bay. While he's relying on the more established species to build his business, he's keen to nurture the natives too.

RODNEY GROVE-JONES, EP SHELLFISH: If people really want them and are prepared to pay for them, we'll produce them.

KERRY STAIGHT: He may see the value in them now, but in the '80s he was involved in a study that gave the angasis the thumbs down and the expansion of the Pacific oyster industry the green light.

RODNEY GROVE-JONES: At the time there was a very small number of people growing oysters in SA, so what we did was put native oysters, angasis, and Pacific oysters out in various places around the state and compared their growth. What we found was that they - in general, the Pacific oysters grew faster and lived - survived better than the natives.

KERRY STAIGHT: Back then, around 90 per cent of Pacific oysters made it to a saleable size, while only 60 per cent of angasis did.

But Brendan Guidera is now noticing he's chucking out a lot more Pacifics than he used to.

BRENDAN GUIDERA: The mortality rate has gone up a lot in the last five or six years with the Pacific oyster. We think it's got quite a bit to do with selective breeding of the spat. People always want to get a quicker-growing, better-shaped oyster, but we think that's come at a cost of survivability.

RODNEY GROVE-JONES: Personally I believe a lot is in handling and that the - now that the bays are fully stocked, and if there's a fluctuation in the feed levels in the water, the oysters aren't feeding as well, they're going to become susceptible to secondary issues.

KERRY STAIGHT: While opinions vary on why survival rates have dropped, there's a deadly disease that is potentially a much bigger threat to the livestock out here: Pacific Oyster Mortality Syndrome, or POMS.

The virus was first found in France in 2008 and there have since been outbreaks in three estuaries in NSW. Now, it doesn't pose a threat to human health, but it does kill Pacifics, and quickly. South Australian waters have so far remained free of the disease, but relying on this oyster no longer seems such a safe bet.

A POMS-resistant oyster is in the works, but is unlikely to surface for another four years. In the meantime, growers need a Plan B and the angasi not only fetches a premium, it can't catch the virus.

JILL COATES: POMS has been the catalyst for us to think about diversifying.

KEN ROWE, KANGAROO ISLAND SHELLFISH: It's probably the number one worry in the oyster industry as a whole, but like I was saying, in SA we'd like to think that maybe we wouldn't get it, but we'd be silly to not plan for it.

KEN ROWE: We are a subtidal farm, so we're going to put them in there and the oyster themselves are a subtidal species, whereas Pacific oysters are an intertidal species. So, angasis are more subtidal, so we're hoping that they might do well.

KERRY STAIGHT: While the angasis give South Australian growers a chance to diversify and access new markets, they give Victoria an opportunity to enter the farmed oyster industry for the first time. And it's an opportunity several Port Phillip Bay mussel producers have seized, even setting up their own hatchery.

PETER LILLIE, BAY SEA FARMS: I've always been interested in growing other things apart from mussels. We've got 90 hectares of water here, which is huge, so we can grow a fair swag of mussels. The problem with them is that it's a competitive game and there's a lot of people growing them.

KERRY STAIGHT: There are not a lot of people growing oysters. Farming Pacifics is banned in Victoria because they're not a native species, but, as in Coffin Bay, angasis are endemic. However, the water out here is deeper, so he has to grow them differently. At the moment, he's experimenting with a couple of techniques, including gluing them onto ropes which hang off lines in the water.

PETER LILLIE: These have been out here, glued on in about February, and they would have had another probably eight months in the cages prior to that. I'm sold! I'm sold on them!

You grow them on a rope, they've just got a clean run of the water coming straight into them. There's no obstruction. If they're in a cage, there's going to be some on top of another and you're going to get smaller ones trapped under big ones and they'll stay small, the big ones'll get bigger. We think, gluing them on, you can clearly see they grow quicker, but can you imagine the work involved with it? Very labour-intensive.

KERRY STAIGHT: Something else that adds to the workload is the washing. Port Phillip Bay is prone to fouling and if the oysters are going to grow, that muck needs to come off.

Disease is also a threat. While angasis may be immune to POMS, they are susceptible to Bonamia, a parasite which is often present in the water and has caused widespread losses in Europe.

PETER LILLIE: It has been detected across the other side of the bay, but it hasn't been an issue with oysters that have been growing, so we haven't seen a mortality incident as a result of it and all the testing we've done on this side, it's been totally clear of it. So touch wood on that one.

KERRY STAIGHT: This year he's hoping to harvest around 50,000 of the native shellfish. He reckons he'll need to up that to 500,000 for this business to really take off. But despite the hurdles ahead, he's got a taste for Australia's flat oyster, and he reckons, in time, others will too.

PETER LILLIE: When we sell off the piers and things, we've been putting these ones against the Pacifics and people are very interested to try them. When they do, they go, "How good are these things?!?!" The potential of it is huge. We're out here. We're sort of mad and keen, so, we'll keep going.